One of the characteristics of the batteries used in a hearing aid is the relatively high internal impedance for this type of voltage source. Furthermore during the lifetime of the battery this impedance increases. As an example the internal impedance for a fresh battery may start at 1-2 Ohm (at 100 Hz) and increase to perhaps 10 Ohm at the end of the lifetime. Another and even worse problem is related to the most common battery type for hearing aids, namely the zinc-air battery. As the name implies one of the active ingredients for operation is air. The amount of air needed is dependent on the current supplied from the battery and if a certain current limit is exceeded the airflow through the inlets of the battery becomes insufficient. As a result the battery voltage starts to drop. To make it worse this current limit is not the same for different battery manufacturers and is also a function of time.
For some hearing aids the above weaknesses is a major problem. If the maximum current consumption from the hearing aid is being limited to a conservative magnitude in order to avoid problems with the battery voltage drop, the maximum sound pressure, which the hearing aid can supply will be clearly below the needs for some of the hearing impaired. Increasing the maximum current on the other hand will especially for modern hearing aids with an EEPROM memory give another problem. For these hearing aids applies that if the battery voltage is below a certain limit, the settings of the hearing aid can not be guaranteed and a reset of the digital control circuit must be carried out—during which the hearing aid is inoperative. In other words some type of control within the hearing aid is needed, which will allow the hearing aid to profit from the high current, which the best zinc-air batteries can deliver, but on the other hand restricts the current demand from the hearing aid if the battery voltage starts to drop.
The objective is to provide a power consumption management method and a power consumption system that remedies these drawbacks of existing battery powered systems.